Major venous anomalies complicating retroperitoneal surgery.

Transposition of the inferior vena cava, duplication of the inferior vena cava, circumaortic renal collar, and retroaortic renal vein constitute the four most common major venous anomalies occurring in the retroperitoneum. Recent clinical cases are presented to review the embryogenesis, incidence, and clinical importance of these anomalies and to alert the unfamiliar surgeon to their possible existence. A high index of suspicion on the part of the surgeon is required to prevent inadvertent injury to these anomalous veins and to avoid significant hemorrhage during retroperitoneal surgery.